Dehydration of water containing source of formaldehyde, and a method for producing an ethylenically unsaturated carboxylic ester

ABSTRACT

Disclosed are methods for dehydrating a water containing source of formaldehyde in which water is separated from the water containing source of formaldehyde using a zeolite membrane. In certain aspects, the water containing source of formaldehyde includes a separation enhancer having a relative static permittivity ranging from 2.5 to 20, and the water containing source of formaldehyde may further include methanol. In certain aspects, (meth)acrylic acid alkyl ester may be produced using the dehydrated source of formaldehyde.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. National Stage Application claims priority fromPCT/JP2013/054639 filed Feb. 18, 2013, which claims priority fromPCT/JP2012/054498 filed Feb. 17, 2012, the entirety of which areincorporated herein be reference.

TECHNICAL FIELD

The present invention relates to a method for dehydration of watercontaining source of formaldehyde, and a method for producing(meth)acrylic acid alkyl ester.

BACKGROUND ART

Recently, a method for producing (meth)acrylic acid alkyl ester byreacting a carboxylic acid ester with formaldehyde in the presence of acatalyst (vapor-phase condensation reaction) has been developed. Forexample, when methyl propanoate is used as carboxylic acid ester, methylmethacrylate is obtained as shown in the following formula (I).CH₃—CH₂—COOCH₃+HCHO→CH₃—CH(CH₂OH)—COOCH₃→CH₃—C(CH₂)—COOCH₃+H₂O  (I)

Formaldehyde is used in the form of formalin in many cases. Formalin isan aqueous solution containing formaldehyde, and generally containsmethanol as a stabilizer. Therefore, when formalin is used as a rawmaterial of (meth)acrylic acid alkyl ester, water is introduced into thereaction system. When water is present in the reaction system,inhibition of the reaction progression and deterioration of the catalystare more likely to occur.

A further reaction with an acetal is shown in the following formula(II).R³—CH₂—COOR⁴+R′OCH₂OR″→R³—C(:CH₂)—COOR⁴+R′OH+R″OH   (II)

A theoretical example of formula (II) with a dimethoxymethane is shownin the following formula (III).CH₃—CH₂—COOR⁴+CH₃OCH₂OCH₃→CH₃—C(:CH₂)—COOR⁴+2CH₃OH   (III)

The use of dimethoxymethane thus theoretically provides an anhydroussystem which avoids the difficulty of subsequent water separation and/orsubsequent product hydrolysis. In addition, the use of dimethoxymethaneavoids the use of free formaldehyde but nevertheless acts in a generalsense as a source of formaldehyde. The absence of water and freeformaldehyde could greatly simplify the separation of methylmethacrylate from the product stream.

However, in practice, formula (III) is problematic because methanoldehydrates to dimethyl ether and water. In addition, dimethoxymethanedecomposes under catalytic conditions to dimethylether and formaldehyde.Any water formed in these reactions can hydrolyse the ester feedstock orproduct to its corresponding acid which may be undesirable.

In addition, the presence of water in the reaction mixture increasescatalyst decay so that the presence of water may be undesirable even inthe production of ethylenically unsaturated carboxylic acids.

Therefore, when (meth)acrylic acid alkyl ester is produced, there is ademand to reduce the amount of water which is introduced to the reactionsystem, and, for example a method of dehydration by distillation of anaqueous solution of formaldehyde has been proposed (see PTL 1).

CITATION LIST Patent Literature

[PTL 1] JP-A-2006-265123

SUMMARY OF INVENTION Technical Problem

However, the method disclosed in PTL 1 had an insufficient dehydrationperformance.

The present invention is made from the viewpoint of these problems, andit provides a method for dehydration of a water containing source offormaldehyde having an excellent dehydration performance, and a methodfor producing (meth)acrylic acid alkyl ester using a dehydrated sourceof formaldehyde obtained by dehydration of the water containing sourceof formaldehyde.

Solution to Problem

According to a first aspect of the present invention, there is provideda method for dehydration of a water containing source of formaldehydecomprising the step of contacting the source of formaldehyde with azeolite membrane in a manner effective to separate at least part of thewater from the source of formaldehyde wherein the water containingsource of formaldehyde comprises a separation enhancer having a relativestatic permittivity of between 2.5 and 20 at 20° C. and atmosphericpressure and wherein the water containing source of formaldehyde furthercontains methanol.

Preferably, the water is separated from the said water containing sourceof formaldehyde by zeolite membrane pervaporation or zeolite membranevapor permeation, and more preferably, the water is separated by vaporpermeation.

Typically, in the process of the invention, the water enriched fluid isthe permeate and the dehydrated source of formaldehyde is the retentate.However, it is possible for the dehydrated source of formaldehyde to bethe permeate and the water enriched fluid to be the retentate.

According to a further aspect of the present invention there is provideda method for producing an ethylenically unsaturated carboxylic ester,preferably, an α, β ethylenically unsaturated carboxylic ester bycontacting a source of formaldehyde with a carboxylic acid ester in thepresence of a catalyst, wherein a dehydrated source of formaldehyde isobtained by contacting a water containing source of formaldehyde with azeolite membrane in a manner effective to separate at least part of thewater from the water containing source of formaldehyde to produce thesaid dehydrated source of formaldehyde and the dehydrated source offormaldehyde is used as the said source of formaldehyde for the saidmethod.

A particular preferred feature of the further aspect of the presentinvention is that the water containing source of formaldehyde contains aseparation enhancer having a relative static permittivity of between 2.5and 20, more preferably and according to the first or further aspects ofthe present invention the relative static permittivity is between 3 and15, and most preferably between 4 and 10, especially, between 4 and 8 at20° C. and atmospheric pressure.

By “atmospheric pressure” herein is meant 101.325 kPa.

By “relative static permittivity” is meant the ratio of the electricfield strength in a vacuum to that in a given medium at a frequency ofzero, this is commonly known as the dielectric constant.

It has been found that the separation enhancer carboxylic acid ester isparticularly effective. The carboxylic acid ester is preferably methylpropanoate, methyl acrylate, methyl methacrylate, ethyl ethanoate ormethyl ethanoate, more preferably, the carboxylic acid ester is methylpropanoate or methyl ethanoate, and most preferably, the carboxylic acidester is methyl propanoate.

A preferred feature of the further aspect of the present invention isthat a water containing source of the separation enhancer is combinedwith the water containing source of formaldehyde to produce a combinedsource and wherein the combined source is dehydrated in accordance withthe first or further aspect of the invention to provide the saiddehydrated source of formaldehyde which contains a separation enhancer.Whether the water containing source of formaldehyde is combined orotherwise, it may be contacted with the zeolite membrane in a batchprocess, a recycled batch process (i.e. repeated exposure of the samebatch) or a continuous process. In a continuous process, a series ofzeolite treatments with two or more membranes in series is alsoenvisaged.

In preferred embodiments, the water containing source of formaldehydeand, optionally, the water containing source of the separation enhancercontains methanol.

It will be appreciated from the foregoing that the separation enhanceris not methanol. Typically, the separation enhancer is not a C1-C5 alkylalcohol, more typically, it is not an alkyl alcohol, most typically, itis not an alcohol.

Typically, the ethylenically unsaturated ester is selected from the listconsisting of methyl methacrylate and methyl acrylate.

The zeolite membrane is preferably a Linde Type-A zeolite membrane, morepreferably, a Linde type-4A zeolite membrane.

The concentration of water in the water containing source offormaldehyde is preferably 0.5% by mass or more.

[1] A method for dehydrating a water containing source of formaldehydecomprising:

contacting the source of formaldehyde with a zeolite membrane in amanner effective to separate at least part of the water from the sourceof formaldehyde, wherein the water containing source of formaldehydecomprises a separation enhancer having a relative static permittivity ofbetween 2.5 and 20 at 20° C. and atmospheric pressure and wherein thewater containing source of formaldehyde further contains methanol.

[2] The method for dehydrating a water containing source of formaldehydeaccording to [1], wherein the manner is selected from the groupconsisting of zeolite membrane pervaporation or zeolite membrane vaporpermeation.

[3] The method for dehydrating a water containing source of formaldehydeaccording to [2], wherein water is separated from the water containingsource of formaldehyde by zeolite membrane vapor permeation.

[4] The method for dehydrating a water containing source of formaldehydeaccording to any one of [1] to [3], wherein the separated water is apermeate and, a dehydrated source of formaldehyde is a retentate.

[5] The method for dehydrating a water containing source of formaldehydeaccording to any one of [1] to [4], wherein the separation enhancer iscarboxylic acid ester.

[6] The method for dehydrating the water containing source offormaldehyde according to claim 5, wherein the carboxylic acid ester isselected from methyl methacrylate, methyl acrylate, methyl propanoateethyl ethanoate or methyl ethanoate.

[7] The method for dehydrating the water containing source offormaldehyde according to claim 6, wherein the carboxylic acid ester ismethyl propanoate.

[8] The method for dehydrating the water containing source offormaldehyde according to any one of [1] to [7], wherein the zeolitemembrane is a Linde Type-A or chabazite zeolite membrane.

[9] The method for dehydrating the water containing source offormaldehyde according to [8], wherein the zeolite membrane is a LindeType-4A zeolite membrane.

[10] The method for dehydrating the water containing source offormaldehyde according to any one of [1] to [9], wherein theconcentration of water in the water containing source of formaldehyde isat least 0.5% by mass based on 100% by mass of the water containingsource of formaldehyde.

[11] A method for producing an ethylenically unsaturated carboxylicester, preferably, an α, β ethylenically unsaturated carboxylic ester,comprising: contacting a dehydrated source of formaldehyde with acarboxylic acid ester in the presence of a catalyst,

wherein the dehydrated source of formaldehyde is obtained by contactinga water containing source of formaldehyde with a zeolite membrane in amanner effective to separate at least part of the water from the watercontaining source of formaldehyde to produce the said dehydrated sourceof formaldehyde.

[12] The method for producing an ethylenically unsaturated carboxylicester according to [11], wherein the water containing source offormaldehyde further comprises a separation enhancer having a relativestatic permittivity of between 2.5 and 20 at 20° C. and atmosphericpressure.

[13] The method for producing an ethylenically unsaturated carboxylicacid ester according to [12] comprising: combining a water containingsource of the separation enhancer with the water containing source offormaldehyde to produce a combined source, and dehydrating the combinedsource in accordance with the method for dehydrating the watercontaining source of formaldehyde according to [11] to provide adehydrated source of formaldehyde which contains the separationenhancer.

[14] The method for producing an ethylenically unsaturated carboxylicacid ester according to any one of [12] to [13], wherein the separationenhancer is carboxylic acid ester.

[15] The method for producing an ethylenically unsaturated carboxylicacid ester according to any one of [11] to [14], wherein the watercontaining source of formaldehyde further contains methanol.

[16] The method for producing an ethylenically unsaturated carboxylicacid ester according to any one of [13] to [15], wherein the watercontaining source of the separation enhancer further contains methanolin addition to the separation enhancer.

[17] The method for producing an ethylenically unsaturated carboxylicacid ester according to any one of [11] to [16], wherein theethylenically unsaturated acid ester is selected from the groupconsisting of methyl methacrylate and methyl acrylate.

Advantageous Effects of Invention

The present invention can provide a method for dehydration of the watercontaining source of formaldehyde having an excellent dehydrationperformance and a method for producing (meth)acrylic acid alkyl ester byusing a dehydrated source of formaldehyde obtained by such dehydration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration view showing one example of aseparation device where water is separated from the water containingsource of formaldehyde.

FIG. 2 is a schematic configuration view showing a further example of aseparation device where water is separated from the water containingsource of formaldehyde.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.

A method for dehydration of the water containing source of formaldehyde(hereinafter, simply referred to as “dehydration method”) of the presentinvention separates water from water containing source of formaldehydeby using a zeolite membrane.

In the invention, a water containing source of formaldehyde is definedas a solution containing formaldehyde, water and an organic solventother than formaldehyde. An example of a dehydrated source offormaldehyde is a solution where at least some water has been separatedfrom the water containing source of formaldehyde. Generally herein, a“dehydrated source of formaldehyde” refers to a water containing sourceof formaldehyde that has had at least some water removed by the methodof the present invention.

The water containing source of formaldehyde contains formaldehyde andwater. Since formaldehyde is easily polymerized, the water containingsource of formaldehyde preferably contains an organic solvent other thanformaldehyde, for preventing polymerization of formaldehyde in the watercontaining source of formaldehyde. The organic solvent other thanformaldehyde is not specifically limited, and various organic solventscan be used. Typically, however, by “organic solvents” mentioned hereinis not meant the separation enhancer described below. A preferredorganic solvent is methanol. However, generally, a preferred solvent isa compound with which the formaldehyde forms a weak or strong complexwhich reduces the activity of formaldehyde towards polymerization.

The water containing source of formaldehyde is available in the form offormalin. Commercially available formalin contains methanol as astabilizer.

The content of formaldehyde is not specifically limited, but ispreferably 5 to 70% by mass with respect to 100% by mass of watercontaining source of formaldehyde. When commercially available formalinis used as the water containing source of formaldehyde, the content offormaldehyde is generally 37% by mass or more. When the content offormaldehyde is low, for instance, below 5%, and the formaldehyde isused as a raw material in the reaction of producing (meth)acrylic acidalkyl ester, a sufficient yield is not obtained. When the content offormaldehyde is high, for instance, above 50%, a polymerization reactionof formaldehyde may occur and stability tends to deteriorate.Accordingly, a preferred range for the content of formaldehyde is up toless than 20% by weight, more preferably, 5-18% by weight, mostpreferably, 5-15% by weight in the water containing source offormaldehyde. When a combined water containing source of formaldehydeand water containing source of separation enhancer is used, the overallformaldehyde level in the combined stream is preferably, 2 to 70% bymass with respect to 100% by mass of the water containing combinedstream. Again, a preferred range for the content of formaldehyde is upto less than 20% by weight, more preferably, 3-18% by weight, mostpreferably, 5-15% by weight in the water containing combined stream.

On the other hand, the content of organic solvent in the combined watercontaining source of formaldehyde and water containing source ofseparation enhancer other than formaldehyde is preferably 5 to 90% bymass of 100% by mass of combined water containing source of formaldehydeand water containing source of separation enhancer. When the content ofthe organic solvent other than formaldehyde is lower than 5% by mass,the formaldehyde may not be sufficiently stable. When the content of theorganic solvent other than formaldehyde is higher than 90% by mass, theconcentration of the raw material for producing (meth)acrylic acid alkylester is lowered, and thus a sufficient yield tends not to be obtained.

In the present invention, when water is separated from water containingsource of formaldehyde using a zeolite membrane, separation enhancer isor is preferably added to the water containing source of formaldehyde.Thereby, the dehydration performance is increased. The separationenhancer may be in solution with an organic solvent such as methanol. Inaddition, the separation enhancer may be in solution with water.Preferably, the separation enhancer is in solution with water andmethanol. Accordingly, the separation enhancer may be added as a watercontaining, and optionally, methanol containing, source of separationenhancer. Accordingly, the combined water containing source offormaldehyde and separation enhancer may contain methanol as well aswater.

The content of separation enhancer is preferably 10% by mass or more,more preferably 20% by mass or more, with respect to 100% by mass ofwater containing source of formaldehyde. When the amount of separationenhancer is lower than 10% by mass, it is hard to obtain a sufficientdehydration performance. The upper limit of the amount of separationenhancer added is not specifically limited, but is preferably 90% bymass or less, and more preferably 80% by mass or less.

The preferred separation enhancers are preferably medium polaritysolvents.

Suitable separation enhancers may be selected from trifluoromethane,m-difluorobenzene, fluorobenzene, trifluoromethylbenzene,o-fluorotoluene, m-fluorotoluene, p-fluorotoluene,1,3-bis(trifluoromethyl)benzene; methyl methanoate, ethyl methanoate,methyl ethanoate, methyl acrylate, propyl methanoate, ethyl ethanoate,methyl propanoate, ethyl acrylate, methyl trans-2-butenoate, methylmethacrylate, dimethyl malonate, butyl methanoate, isobutyl methanoate,propyl ethanoate, ethyl propanoate, methyl butanoate, ethyl 2-butenoateethyl methacrylate, diethyl oxalate, dimethyl succinate, ethylene glycoldiacetate, pentyl methanoate, isopentyl methanoate, butyl ethanoate,tert-butyl ethanoate, propyl propanoate, ethyl butanoate, methylpentanoate, ethylene glycol monoethyl ether acetate, cyclohexylmethanoate, butyl acrylate, diethyl malonate, dimethyl glutarate,1,2,3,-propanetriol-1,3-diacetate, pentyl ethanoate, butyl propanoate,propyl butanoate, ethyl pentanoate, ethyl 3-methylbutanoate, methylhexanoate, benzyl methanoate, phenyl ethanoate, methyl benzoate, methylsalicylate, diethyl maleate, diethyl fumarate, methylcyclohexanecarboxylate, cyclohexyl ethanoate, diisopropyl oxalate,diethyl succinate, dimethyl adipate, hexyl ethanoate, pentyl propanoate,isopentyl propanoate, butyl butanoate, propyl pentanoate, ethylhexanoate, methyl heptanoate, ethyl benzoate, methyl 4-methylbenzoate,benzyl ethanoate, phenyl propanoate, ethyl salicylate, methyl2-methoxybenzoate, triacetin, cyclohexyl propanoate, ethylcyclohexanecarboxylate, diethyl glutarate, heptyl ethanoate, pentylbutanoate, methyl octanoate, methyl 2-(acetyloxy)benzoate, dimethylphthalate, 2-phenylethyl ethanoate, benzyl propanoate, phenylpropanoate, propyl benzoate, ethyl phenylacetate, cyclohexyl butanoate,diethyl adipate, octyl ethanoate, 2-methylheptyl ethanoate, pentylpentanoate, ethyl trans-cinnamate, benzyl butanoate, phenyl pentanoate,butyl benzoate, pentyl hexanoate, propyl cinnamate, diethyl phthalate,pentyl benzoate, pentyl salicylate, 1-bornyl ethanoate, dibutyltartrate, phenyl salicylate, hexyl benzoate, diethyl nonanedioate,benzyl benzoate, benzyl salicylate, pentyl cinnamate, diisobutyladipate, diethyl sebacate, phenyl 2-(acetyloxy)benzoate, tributyrin,dibutyl phthalate, 2-naphthyl salicylate, dipentyl phthalate,dicyclohexyl adipate, dibutyl sebacate, dihexyl phthalate,1,2,3-propanetriyl hexanoate, butyl oleate, dioctyl phthalate, dioctylsebacate; 2-methyl-2-butanol, 2,2-dimethyl-1-propanol,1-methylcyclopentanol, 3-hexanol, 3-methyl-3-pentanol,2-ethyl-1-butanol, o-cresol, cyclohexanemethanol, 2-methylcyclohexanol,2-heptanol, 3-heptanol, 4-heptanol, 3-methyl-2-hexanol,2,2-dimethyl-1-pentanol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol,2,6-xylenol, 3,4-xyleno, 3,5-xylenol, 1-phenylethanol, 2-octanol,3-octanol, 4-octanol, 2-methyl-1-heptanol, 4-methyl-1-heptanol,5-methyl-1-heptanol, 3-methyl-2-heptanol, 5-methyl-2-heptanol,6-methyl-2-heptanol, 3-methyl-4-heptanol, 2-ethyl-1-hexano,2,2-dimethyl-1-hexano, 2,2-dimethyl-1-hexanol, 1-phenyl-1-propanol,2-phenyl-2-propanol, 1-phenyl-2-propanol, 1-nonanol, 2-nonanol,3-nonano, 1-naphthol, 2-naphthol, 1-phenyl-2-methyl-2-propanol, thymol,1-decanol, 2-decanol, 3-decanol, 2,2-dimethyl-1-octanol, 1-undecanol,1-dodecanol, 1-tridecano, 1-tetradecanol; dimethyl ether,ethoxyacetylene, tetrahydrofuran, diethyl ether, ethylene glycoldimethyl ether, tetrahydropyran, 2-methyltetrahydrofuran,phenoxyacetylene, butoxyacetylene, diethylene glycol dimethyl ether,anisole, triethoxymethane, ethyl phenyl ether, 1,2-dimethoxybenzene,1,3-dimethoxybenzene, 1,4-dimethoxybenzene, triethylene glycol dimethylether, eucalyptol, tetraethylene glycol dimethyl ether,1-methoxynaphthalene; 1,4-cyclohexanedione, 2-octanone, 2-nonanone,di-tert-butyl ketone, 2,6-dimethyl-4-heptanone, 2-decanone,2-undecanone, 7-tridecanone, 9-heptadecanone, 10-nonadecanone; pentanal,2,2-dimethylpropanal and 1-heptanal; or selected from the above listexcluding C1-C5 alkyl alcohols; or selected from the above listexcluding alkyl alcohols; or selected from the above list excludingalcohols.

In addition, the separation enhancer extends to mixtures of two or moreof the above listed solvents or mixtures of one or more of the abovelisted solvents with one or more other solvents which mixtures in eithercase have relative static permittivity falling within the ranges definedabove at 20° C. and atmospheric pressure.

The separation enhancer is preferably a carboxylic acid esterrepresented by the following formula (IV).R¹—COOR²  (IV)

In formula (IV), R¹ is a hydrogen atom or an organic group, and theorganic group is preferably an organic group having 1 to 4 carbon atoms.The organic group is a group essentially having a carbon atom, and forexample includes an alkyl group, or an alkoxy group.

R² is an alkyl group, and the alkyl group is preferably an alkyl grouphaving 1 to 4 carbon atoms.

Specific examples of the carboxylic acid ester include methylpropanoate, methyl methacrylate, methyl acrylate, methyl ethanoate, orethyl ethanoate. Of these, when methyl propanoate or ethyl ethanoate isused as a separation enhancer, a permeation flux tends to be increased.In addition, methyl propanoate can be used as a raw material of areaction which produces methyl methacrylate by reaction of formaldehydeand methyl propanoate, and therefore methyl propanoate is particularlypreferable in the present invention.

The water containing source of formaldehyde is subjected to dehydrationusing a zeolite membrane.

The zeolite membrane is a membrane having excellent separation, heatresistance, and chemical resistance properties.

Examples of the zeolite membrane include a Linde Type-A (LTA) zeolitemembrane, a T-type (ERI-OFF) zeolite membrane, a X-type (FAU) zeolitemembrane, a Y-type (FAU) zeolite membrane, a mordenite (MOR) membrane, aZSM-5 (MFI) zeolite membrane, a BEA zeolite membrane, a chabazitemembrane (CHA), and a silicalite membrane. The structures of thesezeolites are described in “The Atlas of Zeolite Framework Types”, 6^(th)revised edition, by Ch Baerlocher, L B McCusker and D H Olsen, Elsevier,ISBN 978-0-444-53064-6. Of these, a Linde Type-A zeolite membrane, aT-type zeolite membrane, a chabazite membrane (CHA), a X-type zeolitemembrane and a Y-type zeolite membrane are preferable. From theviewpoint that water can be selectively separated from the watercontaining source of formaldehyde, a Linde Type-A zeolite and achabazite (CHA) membrane having high Al content is preferable.

In addition, the present invention provides advantageously high fluxrates.

Generally, as a zeolite type, the higher the Al content, the more theaffinity to water is increased, and the more the dehydration performancetends to be improved.

The concentration of water in the water containing source offormaldehyde is typically 25% by mass or less, more typically, 20% bymass or less. When Linde Type-A zeolite membrane is used as zeolitemembrane, from the viewpoint of water resistance thereof, aconcentration of water in water containing source of formaldehyde ispreferably 15% by mass or less, more preferably 10% by mass or less.When a concentration of water in water containing source of formaldehydeis more than 15% by mass, deterioration of separation performance mayoccur due to the deterioration of the Linde Type-A zeolite membrane.However, if the concentration of water in the water containing source offormaldehyde is reduced, the permeation flux tends to be reduced.Therefore, the concentration of water in the water containing source offormaldehyde irrespective of membrane is preferably 0.5% by mass ormore, more preferably 2% by mass or more, and even more preferably 5% bymass or more based on 100% by mass of the water containing source offormaldehyde.

The amount of zeolite is sufficient to dehydrate the water containingsource of formaldehyde by preferably at least 10%, more preferably atleast 20%, and most preferably at least 30%. Typically, more than 50% ofthe total water present is separated from the water containing source offormaldehyde.

Generally, the higher the Si/Al molar ratio in a zeolite composition,the more the water separation performance tends to decrease. Incomparison with Linde Type-A zeolite (Si/Al≈1.0), T-type zeolite(Si/Al=3.6) and a mordenite (Si/Al=5.1) have a lower water separationperformance. The Si:Al molar ratio ranges for the zeolite membrane arepreferably between 1:1 and 10:1, more preferably between 1:1 and 9:1.

The Linde Type-A zeolite membrane can be formed by precipitating LindeType-A zeolite crystals on the surface of a porous support.

Examples of the porous support include ceramics such as alumina, silica,zirconia, silicon nitride, and silicon carbide, metals such as aluminumand stainless steel, and polymers such as polyethylene, polypropylene,and polytetrafluoroethylene. From the viewpoint of the separationperformance of the membrane, inorganic compounds such as ceramics ormetals are preferable. The shape of the porous support is notspecifically limited, but a tube shape is preferable.

A method where a Linde Type-A zeolite crystal is precipitated on thesurface of a porous support includes a method in which a Linde Type-Azeolite seed crystal is applied on the surface of the support, followedby precipitation by a synthesis method such as a hydrothermal synthesismethod or a vapor phase method, in the presence of a silica raw material(for example, sodium silicate, silica gel, silica sol, silica powder, orthe like) and/or an alumina raw material (for example, sodium aluminate,aluminum hydroxide, or the like). The Linde Type-A zeolite can be in theform of its sodium salt in which form it is usually synthesized or canbe ion exchanged with solutions of metal ions, for examples, chloride ornitrate salts, particularly potassium or calcium ions or mixtures ofthese with sodium ions. Preferably part of the sodium ions are ionexchanged with calcium ions to produce the structure known as LindeType-5A zeolite. Most preferably the Linde Type-A zeolite is in the 100%sodium form known as Linde Type-4A zeolite.

X-type and Y-type zeolites are preferably in their sodium forms or acidforms, more preferably, the sodium forms.

Chabazite type zeolites may be preferably in the form of acid, sodium,potassium, calcium or strontium, more preferably sodium, potassium orcalcium. A commercially available product can be used as the LindeType-A zeolite membrane.

As mentioned above, a method of separating water from a water containingsource of formaldehyde using a zeolite membrane includes pervaporation,or vapor permeation. From the viewpoint that the size of the device canbe reduced, pervaporation is preferable, whereas from the viewpoint thatconsumption of heat energy can be lowered without being associated withphase transition, vapor permeation is preferable.

As described above, in dehydration by a zeolite membrane, a separationfactor and a permeation flux tend to be increased in accordance withincrease of a concentration of water in the water containing source offormaldehyde. Generally, a permeation flux tends to be increased inaccordance with the rising of temperature of the water containingsource.

In the present invention, the temperature of the water containing sourceof formaldehyde during separation is preferably 0 to 200° C., morepreferably, 30 to 180° C., and most preferably 50 to 150° C.

One example of pervaporation will be specifically described using FIG.1.

FIG. 1 shows a separator 10 for separating water from the watercontaining source of formaldehyde using a zeolite membrane bypervaporation. The separator 10 of the example includes a vessel 11storing an water containing source of formaldehyde, a zeolite membrane12 provided in the vessel 11, and a thermometer 13, a thermostatic bath14 for maintaining the constant temperature of the water containingsource of formaldehyde in the vessel 11, a vacuum pump 15 for reducingpressure inside the decompression line 16 and the zeolite membrane 12, adecompression line 16 connecting the zeolite membrane 12 to vacuum pump15, a first collection device 17 and a second collection device 18provided in the decompression line 16 and a vacuum gauge 19.

In the zeolite membrane 12, one end is sealed and the other end isconnected to the decompression line 16 through a plug 12 a such as astainless steel tube.

Examples of the thermometer 13 include a thermocouple, or the like.

A first collection device 17 and second collection device 18 collectcomponents (permeation solution) separated from the water containingsource of formaldehyde. These devices include Dewar flasks 17 a and 18a, which store a refrigerant for cooling components which permeate azeolite membrane 12 in a vapor state and pass through the first and thesecond collection devices 17 and 18, and trapping tubes 17 b and 18 bfor trapping the component (permeation solution) in a cooled liquidstate or solid state. Examples of the refrigerant include liquidnitrogen.

Specific examples of the pervaporation using a separator 10 shown inFIG. 1 will be described. A case using the Linde Type-A zeolitemembranes as a zeolite membrane 12 is described below.

First, the water containing source of formaldehyde is stored in a vessel11. The temperature of the water containing source of formaldehyde inthe vessel 11 is maintained by thermostatic bath 14 so as to beconstant. The temperature of the water containing source of formaldehydeis preferably 50 to 150° C. In the specific examples below it is 60° C.

Separately, liquid nitrogen is stored in Dewar flasks 17 a and 18 a.

Then, a vacuum pump 15 operates to reduce the pressure of an innerportion of a decompression line 16 and the zeolite membrane 12. Then,water in the water containing source of formaldehyde permeates thezeolite membrane 12 in the form of vapor. The water vapor permeating thezeolite membrane 12 is cooled by liquid nitrogen filled in the Dewarflask 17 a in a first collection device 17 and collected by a trap tube17 b.

The second collection device 18 need not be provided. However, when thesecond collection device 18 is provided, in a case where water vapor isnot collected by the first collection device 17, the water vapor passingtherethrough can be collected by the second collection device 18, andthus infiltration of water into the vacuum pump 15 can be suppressed.

In order to realize efficient membrane separation, it is necessary toprovide a concentration difference in the water at the supply side andat the permeation side in respect to the zeolite membrane. As a specificdevice for providing a concentration difference, one providing apressure difference which is as large as possible between the permeationand supply sides, or one flowing gas other than water so as not toretain water on the permeation side, can be exemplified.

For providing as large a pressure difference as possible, the supplyside may be pressurized, or the permeation side may be depressurized. Inconsideration of ease and permeability, the pressure of the supply sideis preferably 50 to 800 kPa, the pressure of the permeation side ispreferably 15.0 kPa or lower, the pressure of the supply side is morepreferably atmospheric pressure to 500 kPa, and the pressure of thepermeation side is more preferably 5.0 kPa or lower.

As the gas other than water so as not to retain water in the permeationside, in consideration of inertness not reacting with water and ease ofavailability, nitrogen or argon is preferable.

According to the aforementioned method, water can be separated from thewater containing source of formaldehyde. The separated water iscollected in a trapping tube 17 b of the first collection device 17. Onthe other hand, the dehydrated source of formaldehyde is stored in avessel 11.

The aforementioned method permeates water into a zeolite membrane 12,and separates the water from the water containing source offormaldehyde, however, the present invention is not limited thereto. Forexample, when kinds of the zeolite membrane 12 are changed, componentsother than water can be made to permeate the zeolite membrane 12 andseparate from the water containing source of formaldehyde. In this case,the dehydrated source of formaldehyde is collected in the trapping tube17 b of the first collection device 17 as the permeation solution andwater may be retained as the retentate.

The term “a source of formaldehyde” is that free formaldehyde may eitherform in situ from the source under reaction conditions or that thesource may act as the equivalent of free formaldehyde under reactionconditions, for example it may form the same reactive intermediate asformaldehyde so that the equivalent reaction takes place. For theavoidance of doubt the source may itself be free formaldehyde.

A suitable source of formaldehyde may be a compound of formula (V),

wherein R⁵ and R⁶ are preferably independently selected from C₁-C₁₂hydrocarbons or H, X is O, n is an integer from 1 to 100, and m is 1.

R⁵ and R⁶ are independently selected from C₁-C₁₂ alkyl, alkenyl or arylas defined herein, or H, more preferably C₁-C₁₀ alkyl, or H, mostpreferably C₁-C₆ alkyl or H, and especially methyl or H. n is an integerpreferably from 1 to 10, more preferably 1 to 5, and especially 1 to 3.

However, other sources of formaldehyde may be used including trioxane ortrioxane containing sources.

Therefore, a suitable source of formaldehyde includes any equilibriumcomposition which may provide a source of formaldehyde. Examples of suchinclude but are not restricted to dimethoxymethane, trioxane,polyoxymethylenes R¹—O—(CH₂—O)_(i)—R² wherein R¹ and/or R² are alkylgroups or hydrogen, i=1 to 100, paraformaldehyde, formalin(formaldehyde, methanol, water) and other equilibrium compositions suchas a mixture of formaldehyde, methanol and methyl propanoate.

Typically, the polyoxymethylenes are higher formals or hemiformals offormaldehyde and methanol CH₃—O—(CH₂—O)_(i)—CH₃ (“formal-i”) orCH₃—O—(CH₂—O)_(i)—H (“hemiformal-i”), wherein i=1 to 100, preferably i=1to 5, and especially i=1 to 3, or other polyoxymethylenes with at leastone non methyl terminal group. Therefore, the source of formaldehyde mayalso be a polyoxymethylene of formula R³¹—O—(CH2-O—)_(i) R³², where R³¹and R³² may be the same or different groups and at least one is selectedfrom a C₁-C₁₀ alkyl group, for instance R³¹=isobutyl and R³²=methyl.

Preferably, the term formalin is a mixture offormaldehyde:methanol:water in the ratio 25 to 65%:0.01 to 25%:25 to 70%by weight. More preferably, the term formalin is a mixture offormaldehyde:methanol:water in the ratio 30 to 60%:0.03 to 20%:35 to 60%by weight. Most preferably, the term formalin is a mixture offormaldehyde:methanol:water in the ratio 35 to 55%:0.05 to 18%:42 to 53%by weight. Preferably, the mixture comprising formaldehyde, methanol andmethyl propanoate contains less than 50% water by weight. Morepreferably, the mixture comprising formaldehyde, methanol and methylpropanoate contains less than 20% water by weight. Most preferably, themixture comprising formaldehyde, methanol and methyl propanoate contains0.1 to 15% water by weight.

Typically, the water containing source of formaldehyde is a formaldehydesolution comprising formaldehyde, water and, optionally, methanol. Itshould be appreciated that the source of formaldehyde may not containwater, for instance where it is in the form of trioxane or freeformaldehyde, but water may be added by mixing this stream with a secondwater containing source of formaldehyde and/or with a water containingsource of the separation enhancer, such as wet methyl propanoate.

The dehydrated source of formaldehyde obtained by the process of thepresent invention, either as permeate or as retentate from which waterhas been removed as permeate, may be advantageously used as a rawmaterial for producing (meth)acrylic acid alkyl ester.

A method of producing (meth)acrylic acid alkyl ester will be describedbelow as an example.

(Meth)acrylic acid alkyl ester may be obtained by reacting carboxylicacid ester and formaldehyde in the presence of a catalyst in avapor-phase condensation reaction. Therefore, it is possible to use adehydrated source of formaldehyde obtained by the present invention asraw material for the reaction. Since water is sufficiently removed fromthe dehydrated source of formaldehyde, the undesirable introduction ofwater into the reaction system can be reduced. Therefore, suppression ofthe progression of the reaction and deterioration of the catalyst doesnot easily occur.

Examples of the catalyst for this vapor-phase condensation reactioninclude base catalysts, specifically a catalyst where alkali metals suchas potassium, rubidium, and cesium are supported on carriers such assilica, alumina, zirconia, hafnia and combinations thereof.

A suitable molar ratio of carboxylic acid ester to formaldehyde in thevapor-phase condensation reaction is 1:1 to 20:1.

The reaction temperature of the vapor-phase condensation reaction ispreferably 250 to 400° C. and the reaction pressure is preferably 1×10⁵to 1×10⁶ Pa.

Advantageously, when the dehydrated source of formaldehyde containsformaldehyde and carboxylic acid ester, and when the molar ratio in thedehydrated source of formaldehyde is within the aforementioned ratio forthe vapor-phase condensation reaction, lower levels of or no carboxylicacid ester raw material need be added during the reaction. When theratio of carboxylic acid ester in the dehydrated solution is too low orabsent, carboxylic acid ester is added separately to the dehydratedsolution to achieve the necessary level and the solution is subjected tothe vapor-phase condensation reaction.

As the carboxylic acid ester added to the dehydrated source offormaldehyde, the carboxylic acid ester mentioned in the dehydrationmethod of water containing source of formaldehyde can be exemplified.The carboxylic acid ester added to the dehydrated source of formaldehydeis preferably the same as the carboxylic acid ester added to the watercontaining source in the dehydration of the water containing source offormaldehyde.

As the carboxylic acid ester added to the dehydrated source offormaldehyde, a commercially available product or a synthetic compoundmay be used.

The synthesis method of carboxylic acid ester is not specificallylimited, but a synthesis method will be described by an example ofmethyl propanoate.

Ethylene and methanol are reacted with carbon monoxide in the presenceof a catalyst to obtain methyl propanoate (liquid-phase homogeneousreaction).

Examples of the catalysts include a precious metal complex catalyst,specifically a complex catalyst or the like coordinating phosphine orthe like to precious metal.

A reaction temperature of liquid-phase homogeneous reaction ispreferably 10 to 150° C.

A vapor-phase condensation reaction produces water in addition to(meth)acrylic acid alkyl ester which is objective substance by reactingcarboxylic acid ester and formaldehyde. The (meth)acrylic acid alkylester is hydrolyzed by water producing the alcohol appropriate to thestarting ester. Therefore, vapor-phase condensation reaction ispreferably performed in the presence of the appropriate alcohol forsuppressing hydrolysis of (meth)acrylic acid alkyl ester.

When as the carboxylic acid ester, methyl propanoate produced by theaforementioned liquid-phase homogeneous reaction is added to thedehydrated source of formaldehyde and subjected to vapor-phasecondensation reaction, methanol is used in excess, in comparison withethylene, and therefore the resultant methyl propanoate containsunreacted methanol. Since the vapor-phase condensation reaction ispreferably performed in the presence of alcohol, the unreacted methanolneed not be separated from methyl propanoate, and may be provided in thevapor-phase condensation reaction in addition to methyl propanoate.

The dehydrated source of formaldehyde obtained by dehydrating methanoland the water containing source of formaldehyde contains methanol.

Therefore, when the methanol-containing dehydrated solution is used ormethyl propanoate produced by a liquid-phase homogeneous reaction isadded to the dehydrated solution, the vapor-phase condensation reactioncan be performed in the presence of methanol without separate additionof methanol in a reaction system.

The reaction product obtained by vapor-phase condensation reactioncontains water in addition to (meth)acrylic acid alkyl ester which isthe desired product. In vapor-phase condensation reaction, carboxylicacid ester is used in large excess in comparison with formaldehyde, andtherefore the reaction product contains unreacted carboxylic acid ester.Moreover, when vapor-phase condensation reaction is performed in thepresence of the alcohol, the reaction product contains the alcohol.

Therefore, (meth)acrylic acid alkyl ester should be separated from thereaction product.

A method for separating (meth)acrylic acid alkyl ester from the reactionproduct is not specifically limited, and for example the (meth)acrylicacid alkyl ester may be separated by distilling the reaction product.

On the other hand, the residue after separating (meth)acrylic acid alkylester from the reaction product contains unreacted carboxylic acid esterand water. Therefore, when carboxylic acid ester and water are separatedfrom the residue, carboxylic acid ester is recovered and recycled as areactant in the production of (meth)acrylic acid alkyl ester.

The residue of the reaction product above can be used as carboxylic acidester added to water containing source of formaldehyde in theaforementioned dehydration method of the present invention. Accordingly,dehydration of water containing source of formaldehyde and separation ofwater from unreacted carboxylic acid ester can be performed at the sametime.

The dehydrated source of formaldehyde produced when the residue ofreaction product is added to the water containing source of formaldehydeand dehydrated, contains unreacted carboxylic acid ester in addition toformaldehyde. Therefore, when the dehydrated source of formaldehyde isused as raw material of (meth)acrylic acid alkyl ester, unreactedcarboxylic acid ester is reused.

The residue of reaction product is added to the water containing sourceof formaldehyde and dehydrated and the resultant solution containingdehydrated formaldehyde is used as a raw material of (meth)acrylic acidalkyl ester. Thereby, the dehydration method of the present inventioncan be incorporated into a portion of a method for producing(meth)acrylic acid alkyl ester, whereby production costs can be reduced.

As described above, according to the dehydration method of the presentinvention, water can be highly efficiently separated from the watercontaining source of formaldehyde. In particular, when a separationenhancer is added and dehydrated, the dehydration performance isexcellent. In this case, if the permeate is enriched in water then theretentate is enriched, with respect to the separation enhancer and watercontaining source of formaldehyde, in formaldehyde and separationenhancer or if the retentate is enriched in water then the permeate isenriched in formaldehyde and separation enhancer. It is preferred thatthe permeate is enriched in water.

The dehydrated source of formaldehyde obtained by the dehydration methodof the present invention is preferable as a raw material of(meth)acrylic acid alkyl ester. In particular, it is preferable whenmethyl methacrylate is produced from methyl propanoate. Further, whenthe dehydrated source of formaldehyde is used as a raw material, theintroduction of water into the reaction system can be reduced, andtherefore, progress of reaction is not easily suppressed and thecatalyst is not easily deteriorated.

EXAMPLES

Hereinafter, specific description will be given in regard to the presentinvention by giving examples. However, the invention is not limited tothese.

Preparative Example 1

The Linde Type-4A zeolite membranes were prepared generally inaccordance with the examples of EP1930067. Specifically, seed crystalsto assist uniform membrane formation were formed on the support. LindeType-4A zeolite fine particles (seed crystals, particle size: 100 nm)were placed in water and stirred to yield a suspension with aconcentration of 0.5% by weight.

The sealed body was used for this example. Specifically, a tubularporous body made of α-alumina and having opening sections at both endswas prepared. The porous body had a mean pore size of 1.3 μm, an outerdiameter of 12 mm, an inner diameter of 9 mm and a length of 10 cm. Asealing member was tightly fitted in one opening section of the porousbody, and a sealing member penetrated by an open air conduit was tightlyfitted in the other opening section.

The sealed body was immersed in the aforementioned suspension. Theentire porous body was immersed in the suspension, and the tip of theopen air conduit was not immersed in the suspension. The sealed body wasimmersed in the suspension for 3 minutes. The sealed body was then drawnout at a rate of about 0.2 cm/s. The porous body obtained by removingthe sealing members and from the sealed body was dried for 2 hours in athermostatic bath at 25° C., and then dried for 16 hours in athermostatic bath at 70° C. to produce a seed crystal-attached porousbody.

Sodium silicate, aluminum hydroxide and distilled water were mixed toyield a reaction solution. 1 part by mole of alumina (Al₂O₃), 2 parts bymole of silicon dioxide (SiO₂) and 2 parts by mole of sodium oxide(Na₂O) were added to 150 parts by mole of water to yield a reactionsolution. The seed crystal-attached porous body was immersed in thereaction solution and held at 80° C. for 3 hours to form a zeolitemembrane on the surface of the seed crystal-attached porous body.

The obtained zeolite membrane was then cleaned with a brush. Further, itwas immersed for 16 hours in warm water at 40° C. A Linde Type-4Azeolite membrane was thus obtained.

Preparative Example 2

The T-type zeolite membranes were prepared generally in accordance withthe examples of U.S. Pat. No. 6,387,269.

Amorphous silica is introduced with stirring into an aqueous solutioncomprising sodium aluminate, sodium hydroxide and potassium hydroxideand allowed to age for 48 hours. The composition of the solutioncorresponds to the following molar ratios: SiO₂/Al₂O₃=112,OH—/SiO₂=0.77, Na+/(Na++K+)=0.77, and H₂O/(Na++K+)=20.75.

Then a porous tubular support whose surface is provided with seedcrystals of the T-type zeolite is immersed in the above reactionmixture. The support consisted of “Mullite”, had a length of 10 cm, anexternal diameter of 1.2 cm, a thickness of 1.5 mm, a pore diameter of1.3 μm and a porosity of 40%. The average size of seed crystals is 100μm. The quantity of seed crystals on the porous support is 30 mg/cm².The hydrothermal synthesis is carried out for 24 hours at 100° C.,followed by rinsing for 12 hours and drying at 70° C.

Preparative Example 3

CHA-type zeolite membranes were prepared generally by hydrothermalsynthesis via a secondary growth method on the outer surface of a porousα-alumina support. For the avoidance of doubt, by “CHA-type zeolite” wemean to refer to a zeolite having a CHA structure as defined by theInternational Zeolite Association (IZA) and is a zeolite having the samestructure as naturally-occurring Chabazite.

First, seed crystals were attached to a porous α-alumina support toassist uniform membrane formation.

The following was prepared as a reaction mixture for hydrothermalsynthesis in the seeding process. In a mixture containing 12.8 g of 1mol/L-NaOH aqueous solution and 75 g of water, 0.8 g of aluminumhydroxide (containing 53.5 wt % of Al₂O₃, obtained from Aldrich) wasadded and dissolved with stirring to make a transparent solution.Thereto, 10.8 g of an aqueous N,N,N-trimethyl-1-adamantanammoniumhydroxide (TMADAOH) solution (containing 25 wt % of TMADAOH, obtainedfrom Sachem Inc.) was added as an organic template, and 19.2 g ofcolloidal silica (Snowtex-40, obtained from Nissan Chemicals Industries,Ltd.) was further added. This mixture was stirred for 3 hours. ACHA-type zeolite seed crystal of about 0.5 μm was synthesizedhydrothermally at 160° C. for 2 days. A dip-coating technique was usedfor seeding. Specifically, an inorganic porous support was dippedvertically into a flask containing an aqueous suspension of the CHA-typezeolite crystals at a concentration of 1% by weight for a predeterminedtime. It was then dried at 100° C. for about 5 hours producing a seedcrystal-attached porous body.

The following was prepared as a reaction mixture for membranehydrothermal synthesis. In a mixture containing 10.5 g of 1 mol/L-NaOHaqueous solution, 7.0 g of 1 mol/L-KOH aqueous solution and 100.0 g ofwater, 0.88 g of aluminum hydroxide (containing 53.5 wt % of Al₂O₃,obtained from Aldrich) was added and dissolved with stirring to make atransparent solution. Thereto, 2.95 g of an aqueousN,N,N-trimethyl-1-adamantanammonium hydroxide (TMADAOH) solution(containing 25 wt % of TMADAOH, obtained from Sachem Inc.) was added asan organic template, and 10.5 g of colloidal silica (Snowtex-40,obtained from Nissan Chemicals Industries, Ltd.) was further added. Thismixture was stirred for 2 hours. The support attached with the seedcrystal was dipped in the vertical direction in a Teflon (registeredtrademark) made inner cylinder containing the reaction mixture above andafter tightly closing the autoclave, heated at 160° C. for 48 hoursunder self-generated pressure. The system was allowed to cool, and thesupport-zeolite membrane composite was taken out of the reactionmixture, washed and then dried at 120° C. for 5 hours or more. Themembrane samples were calcined to remove the template at a rate of0.1-0.5° C./min. Higher temperatures of 450-500° C. were applied for >20h.

The molar ratio SiO₂/Al₂O₃ of the zeolite membrane was measured bySEM-EDX and found to be 17.

Example 1

Formaldehyde (HCHO), water (H₂O), methanol (MeOH), and methyl propanoate(MeP) were mixed so that the mass ratio (HCHO:H₂O:MeOH:MeP) was10:9:11:70, to prepare a sample (feed solution). Water was separatedfrom the feed solution in accordance with the following methods by usinga separator 10 shown in FIG. 1.

A Linde Type-4A zeolite membrane (manufactured in a manner ofpreparative example 1 above, effective membrane area: 2.64×10⁻³ m²) asthe zeolite membrane 12, and the thermocouples as a thermometer 13 wereprovided in the vessel 11. One end of the zeolite membrane 12 wassealed, and the other end was connected with the decompression line 16through the plug 12 a made of stainless-steel, then, the zeolitemembrane 12 and the vacuum pump 15 were connected by the decompressionline 16. Moreover, the first collection device 17, the second collectiondevice 18, and the vacuum gauge 19 were provided at the middle of thedecompression line 16.

500 ml of previously prepared feed solution was stored in the vessel 11.Then, the temperature of the feed solution in the vessel 11 wascontrolled at the thermostatic bath 14 so that the temperature was 60°C.

The liquid nitrogen was stored in the Dewar flasks 17 a and 18 arespectively.

Then, the vacuum pump 15 was operated for 30 minutes, and pressureinside the decompression line 16 and the zeolite membrane 12 was reducedso that pressure on the permeation side became 3.0 kPa or less. Vaporthat permeated the zeolite membrane 12 was cooled in the firstcollection device 17 with the liquid nitrogen with which Dewar flask 17a was filled, and the permeation liquid was collected in a trap tube 17b.

The separation performance of the zeolite membrane was evaluated toobtain the permeation flux, the concentrations of water in the collectedpermeate and the separation factor in accordance with the followingmethods. The results are shown in Table 1.

(1) Permeation Flux

The mass of the permeate that was collected in the trap tube 17 b afterseparation was measured, and the permeation flux was calculated from thefollowing expression (VI). In the expression (VI), “w” is weight ofpermeate [kg], “A” is the effective membrane area of the zeolitemembrane [m²], and “t” is the permeation time [h]. This permeation fluxis an index that shows the weight of permeate per unit area of themembrane, and per unit time.Permeation flux [kg/m²·h]=w/(A×t)  (VI)(2) Concentration of Water in Permeate

The concentration of water in the permeate was obtained by using agas-chromatograph (detector: TCD (Thermal Conductivity Detector),separation column: porapakQ) at the column temperature of 170° C.

(3) Separation Factor

In the same manner as in the concentration of water in permeate (2)above, the concentration of water in the feed solution was obtained andthe separation factor was calculated from the following expression(VII). In the expression (VII), “X” is concentration of water in thefeed solution [% by mass], and “Y” is concentration of water in thepermeate [% by mass].Separation factor={Y/(100−Y)}/{X/(100−X)}  (VII)

Example 2

Water was separated again by using the zeolite membrane used in example1 from the feed solution in the same manner as in example 1. Then, theseparation performance in the repetitive use of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 3

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared sothat the mass ratio in the aqueous solution (HCHO:H₂O:MeOH:MeP) became10:9:41:40. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 4

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared sothat the mass ratio in the aqueous solution (HCHO:H₂O:MeOH:MeP) became10:9:61:20. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 5

Water was separated from the feed solution in the same manner as inexample 1, except using a T-type zeolite membrane (manufactured in amanner of preparative example 2, effective membrane area: 2.64×10⁻³ m²)as the zeolite membrane, and using an aqueous solution (feed solution)prepared so that the mass ratio in the aqueous solution(HCHO:H₂O:MeOH:MeP) became 10:9:41:40. Then, the separation performanceof the zeolite membrane was evaluated. The results are shown in Table 1.

Example 6

Water was separated from the feed solution in the same manner as inexample 1, except methyl ethanoate (MeAc) instead of the MeP, and usingan aqueous solution (feed solution) prepared so that the mass ratio inthe aqueous solution (HCHO:H₂O:MeOH:MeAc) became 10:9:41:40. Then, theseparation performance of the zeolite membrane was evaluated. Theresults are shown in Table 1.

Example 7

Water was separated from the feed solution in the same manner as inexample 1, except using methyl methacrylate (MMA) instead of the MeP,and using an aqueous solution (feed solution) prepared so that the massratio in the aqueous solution (HCHO:H₂O:MeOH:MMA) became 10:9:41:40.Then, the separation performance of the zeolite membrane was evaluated.The results are shown in Table 1.

Example 8

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared sothat the mass ratio in the aqueous solution (HCHO:H₂O:MeOH:MeP) became11:0.6:12:76.4. Then, the separation performance of the zeolite membranewas evaluated. The results are shown in Table 1.

Example 9

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared sothat the mass ratio in the aqueous solution (HCHO:H₂O:MeOH:MeP) became11:3:12:74. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 10

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared sothat the mass ratio in the aqueous solution (HCHO:H₂O:MeOH:MeP) became10:6:11:73. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 11

Water was separated from the feed solution in the same manner as inexample 1, except the temperature of the feed solution was adjusted to50° C. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 12

Water was separated from the feed solution in the same manner as inexample 1, except the temperature of the feed solution was adjusted to40° C. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 13

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared bymixing HCHO, H₂O and MeOH so that the mass ratio (HCHO:H₂O:MeOH) became10:9:81. Then, the separation performance of the zeolite membrane wasevaluated. The results are shown in Table 1.

Example 14

Water was separated from the feed solution in the same manner as inexample 1, except using an aqueous solution (feed solution) prepared bymixing HCHO, H₂O, MeOH and MeP so that the mass ratio(HCHO:H₂O:MeOH:MeP) became 6:9:15:70. Then, the separation performanceof the zeolite membrane was evaluated. The results are shown in Table 1.

Example 15

Water was separated from the feed solution in the same manner as inexample 14, except using an aqueous solution (feed solution) prepared bymixing HCHO, H₂O, MeOH and 1-pentanol so that the mass ratio(HCHO:H₂O:MeOH:1-Pentanol) became 6:9:15:70. Then, the separationperformance of the zeolite membrane was evaluated. The results are shownin Table 1.

Example 16

Water was separated from the feed solution in the same manner as inexample 14, except using an aqueous solution (feed solution) prepared bymixing HCHO, H₂O, MeOH and 1,4-butanediol so that the mass ratio(HCHO:H₂O:MeOH:1,4-Butanediol) became 6:9:15:70. Then, the separationperformance of the zeolite membrane was evaluated. The results are shownin Table 1.

Example 17

Water was separated from the feed solution in the same manner as inexample 14, except using an aqueous solution (feed solution) prepared bymixing HCHO, H₂O, MeOH and glycerol (1,2,3-trihydroxypropane) so thatthe mass ratio (HCHO:H₂O:MeOH:Glycerol) became 6:9:15:70. Then, theseparation performance of the zeolite membrane was evaluated. Theresults are shown in Table 1.

TABLE 1 Feed solution Concentration Concentration Permeation of water inthe Zeolite Temperature of water flux permeate Separation membrane [°C.] Composition [% by mass] [kg/m2 × h] [% by mass] factor Example 1Linde 60 HCHO/H₂O/MeOH/MeP = 9.0 2.61 99.98 40000 Type-4A 10/9/11/70Example 2 Linde 60 HCHO/H₂O/MeOH/MeP = 9.0 2.46 99.97 31000 Type-4A10/9/11/70 Example 3 Linde 60 HCHO/H₂O/MeOH/MeP = 9.0 1.75 99.93 15000Type-4A 10/9/41/40 Example 4 Linde 60 HCHO/H₂O/MeOH/MeP = 9.0 1.45 99.85000 Type-4A 10/9/61/20 Example 5 T-type 60 HCHO/H₂O/MeOH/MeP = 9.0 0.2198.68 760 10/9/41/40 Example 6 Linde 60 HCHO/H₂O/MeOH/MeAc = 9.0 1.399.91 12000 Type-4A 10/9/41/40 Example 7 Linde 60 HCHO/H₂O/MeOH/MMA =9.0 1.65 99.93 14000 Type-4A 10/9/41/40 Example 8 Linde 60HCHO/H₂O/MeOH/MeP = 0.6 0.33 88.57 1300 Type-4A 11/0.6/12/76.4 Example 9Linde 60 HCHO/H₂O/MeOH/MeP = 3.0 1.35 99.37 5100 Type-4A 11/3/12/74Example 10 Linde 60 HCHO/H₂O/MeOH/MeP = 6.0 1.94 99.67 4700 Type-4A10/6/11/73 Example 11 Linde 50 HCHO/H₂O/MeOH/MeP = 9.0 2.24 99.93 15000Type-4A 10/9/11/70 Example 12 Linde 40 HCHO/H₂O/MeOH/MeP = 9.0 1.7799.88 8100 Type-4A 10/9/11/70 Example 13 Linde 60 HCHO/H₂O/MeOH = 9.00.92 99.45 1800 Type-4A 10/9/81 Example 14 Linde 60 HCHO/H₂O/MeOH/MeP =9.0 2.44 99.98 50663 Type-4A 6/9/15/70 Example 15 Linde 60HCHO/H₂O/MeOH/1- 9.0 2.1 99.95 20090 Type-4A pentanol = 6/9/15/70Example 16 Linde 60 HCHO/H₂O/MeOH/1,4- 9.0 1.11 99.86 7131 Type-4Abutenediol = 6/9/15/70 Example 17 Linde 60 HCHO/H₂O/MeOH/glycerol = 9.00.93 99.89 9080 Type-4A 6/9/15/70

As is apparent from Table 1, in examples 1 to 13, water was able to beseparated from the feed solution (an aqueous solution of formaldehyde)efficiently, and the dehydration performance was excellent.Particularly, the values for the permeation flux and the separationfactor in the examples 1 to 4, 6, 7, 11, 12, 14 and 15 in whichdehydration was performed using the Linde Type-4A zeolite membrane withcontaining the separation enhancer in the aqueous solution, were higherand the separation performance (dehydration performance) was improvedcompared to the example 13 in which dehydration was performed using theLinde Type-4A zeolite membrane without containing the separationenhancer in the aqueous solution.

Moreover, it is confirmed from the results of examples 1 and 2 that theseparation performance is maintained excellently even though the zeolitemembrane is used again.

Therefore, it is especially preferable to apply the present invention tothe process for the production of (meth)acrylic acid alkyl estercomprising reacting carboxylic acid ester with formaldehyde in thepresence of a catalyst, wherein a dehydrated source of formaldehyde isused as a raw material for the above reaction.

Example 18

A feed solution having a HCHO/H₂O/MeOH/MeP mass ratio of 5:10:16:66 wasfed continuously. Water was separated from the feed solution inaccordance with the following method, using a separator as shown in FIG.2.

A 400 mm CHA-type zeolite membrane 20 (manufactured in a manner ofpreparative example 3 above,) was housed in a stainless steel housing21. The top of the membrane which is porous alpha-alumina support wasplugged with a solid stainless steel cylinder 22 and sealed. The bottomof the tube, below the side arm 23, was attached to a hollow metalscrew-threaded plug 24 and sealed to make a process gas tight seal. Theeffective area of the exposed 36 mm membrane length was 1.36×10⁻³ m².

The apparatus was located in an air circulation oven (not shown).Thermally equilibrated feed solution was pumped over the CHA-typezeolite membrane at 1.5 ml/min and 110° C. (3 bar g pressure) throughthe side arm 23. The feed solution passed upwards over the zeolitemembrane surface before exiting through flanged outlet 25 a. A vacuum of3.0. kPa was applied to the outlet 25 b at the base of the stainlesssteel housing 21 to enable components passing through the walls of themembrane 20 (permeate) to be removed out of the apparatus. Permeateliquid was collected into a permeate collection vessel (not shown) andnon-permeate liquid was collected in a non-permeate collection vessel(not shown). Liquids in the collection vessels were sampled foranalysis. The separation performance of the zeolite membrane wasevaluated using analytical methods identical to those described inexample 1.

The feed to be dehydrated by the CHA-type zeolite membrane is given inTable 2.

TABLE 2 Components in Feed Wt % Water 10.2 Formaldehyde 4.9 Methanol15.7 Formal 1 0.23 Isobutyraldehyde 0.27 Methacrolein 0.21 Methylpropanoate 66.23 Methyl isobutyrate 0.77 Methyl methacrylate 1.31 Others0.18

The feed composition was fed continuously for 300 hours and samples ofthe permeate and non-permeate liquid were collected periodically foranalysis. The water content of the non-permeate was measured as3.0%+/−0.1% throughout the 300 hours. The permeate contained 90% waterand 10% methanol with all other components in Table 2 being below theirdetection limits (typically 10 ppm).

The separation factor, for water with respect to organics between thefeed and the permeate as defined in (VII) is 79.2.

The methanol and water in the permeate can easily be separated by aconventional distillation. The level of water in the non-permeate caneasily be reduced by increasing the contact time and linear velocity ofthe solution in contact with the membrane.

INDUSTRIAL AVAILABILITY

The present invention can provide a method for dehydration of the watercontaining source of formaldehyde having an excellent dehydrationperformance and a method for producing (meth)acrylic acid alkyl ester byusing a dehydrated source of formaldehyde obtained by such dehydration.

REFERENCE SIGNS LIST

-   10: separator-   11: vessel-   12: zeolite membrane-   12 a: plug-   13: thermometer-   14: thermostatic bath-   15: vacuum pump-   16: decompression line-   17: first collection device-   18: second collection device-   17 a, 18 a: Dewar flask-   17 b, 18 b: trap tube-   19: vacuum gauge-   20: CHA-type zeolite membrane-   21: stainless steel housing-   22: stainless steel tube over porous α-alumina support-   23: side arm-   24: screw-threaded plug-   25 a, 25 b: flanged outlets

The invention claimed is:
 1. A method for dehydrating a water containingsource of formaldehyde comprising: (i) providing a water containingsource of formaldehyde, a separation enhancer in an amount of at least10% by mass or more with respect to 100% by mass of the water containingsource of formaldehyde, and methanol, the water containing source offormaldehyde having a water concentration ranging from 0.5 to 25% bymass of the water containing source of formaldehyde; (ii) contacting thewater containing source of formaldehyde, separation enhancer, andmethanol with a zeolite membrane, and (iii) separating, by zeolitemembrane pervaporation or zeolite membrane vapor permeation, at least50% of the water from a majority of the water containing source offormaldehyde and from a majority of the separation enhancer therebyproducing a dehydrated source of formaldehyde, the dehydrated source offormaldehyde including the majority of the separation enhancer therein,wherein the separation enhancer has a static permittivity of between 2.5and 20 at 20° C. and atmospheric pressure, wherein the separated waterof step (iii) is a permeate and the dehydrated source of formaldehydeincluding the majority of the separation enhancer therein of step (iii)is a retentate; and wherein the temperature of the water containingsource of formaldehyde during separation is 0 to 200° C.
 2. The methodfor dehydrating the water containing source of formaldehyde according toclaim 1, wherein water is separated from the water containing source offormaldehyde by zeolite membrane vapor permeation.
 3. The method fordehydrating the water containing source of formaldehyde according toclaim 1, wherein the separation enhancer is carboxylic acid ester. 4.The method for dehydrating the water containing source of formaldehydeaccording to claim 3, wherein the carboxylic acid ester is selected frommethyl methacrylate, methyl acrylate, methyl propanoate, ethyl ethanoateor methyl ethanoate.
 5. The method for dehydrating the water containingsource of formaldehyde according to claim 4, wherein the carboxylic acidester is methyl propanoate.
 6. The method for dehydrating the watercontaining source of formaldehyde according to claim 1, wherein thezeolite membrane is a Linde Type-A or chabazite zeolite membrane.
 7. Themethod for dehydrating the water containing source of formaldehydeaccording to claim 5, wherein the zeolite membrane is a Linde Type-4A orchabazite zeolite membrane.
 8. The method for dehydrating the watercontaining source of formaldehyde according to claim 1, wherein theseparated water of step (iii) comprises at least 90 wt % of thepermeate.